Water cooled electrode holder assemblies for electric arc furnaces involve complex electrode clamping assemblies mounted on the distal ends of mast arms which project over the top of a generally cylindrical furnace vessel. Typical such assemblies are seen in Turner U.S. Pat. No. 3,444,305 dated May 13, 1969 and applicant's prior U.S. Pat. No. 4,182,927 dated Jan. 8, 1980. The present invention constitutes certain improvements over the holder assemblies shown and described in such prior patents.
Such holder assemblies normally include three electrodes which are positioned in the center of the cylindrical vessel forming an electrode pitch circle or a circle through which the axes of the electrodes extend, each electrode being equally circumferentially spaced around such pitch circle.
It will be appreciated that the larger the pitch circle, the closer the electrodes are positioned to the cylindrical refractory lined wall of the furnace vessel. It will also be appreciated that the larger the pitch circle diameter, the farther apart are the three electrodes. Thus if the electrodes can be positioned fairly close to each other by reducing the electrode pitch circle diameter, certain advantages in the operation of the furnace may be achieved. Such advantages are positioning the electrodes farther from the refractory lining of the cylindrical wall of the vessel resulting in reduced refractory wear. The relining of any furnace or the repair of that lining is an expensive undertaking resulting in substantial down time for the furnace. Thus if the lining life can be extended, substantial economies are achieved.
In addition, a reduced electrode pitch circle diameter permits more power to be introduced to the electrodes, and also reduces overall reactance allowing more power to be supplied to the electrodes, both providing better furnace efficiency. A reduced pitch circle diameter also results in reduced melting time resulting in more furnace capacity, thus reducing the electrode consumption per ton of molten metal.
It is also desirable in an electrode clamping assembly to utilize a differential clamp such as shown in applicant's prior U.S. Pat. No. 4,182,927, but in a more improved, simplified and compact form, such clamp being positioned on the inboard side of a relatively thin U-shape clamp, in this manner enabling the distal ends of the two outer arms of the three mast arms employed to be angled toward each other and the center mast arm in order to reduce the diameter of the electrode pitch circle.